Method of fabricating electron tubes



p 1965 H. v. KNAUF, JR 3,208,137

METHOD OF FABRICATING ELECTRON TUBES Filed Dec. 8, 1961 4 Sheets-Sheet 1 INVEN TOR.

Sept. 28, 1965 H. v. KNAUF, JR 3,208,137

METHOD OF FABRICATING ELECTRON TUBES Filed Dec. 8. 1961 4 Sheets-Sheet 2 g I INVBNTO fizzy 1147mm B mam/y Sept. 28, 1965 H. v. KNAUF, JR

METHOD OF FABRICATING ELECTRON TUBES 4 Sheets-Sheet 3 Filed Dec. 8, 1961 Sept. 28, 1965 Filed Dec. 8, 1961 H. V. KNAUF,

METHOD OF FABRICATING ELECTRON TUBES 4 Sheets-Sheet 4 a i i INVENTOR. 4144M, .46,

United States Patent 3 208 137 METHOD OF FABRlATlNG ELECTRON TUBES Harry V. Knauf, Jr., Mountainside, N.J., assignorto Radio Corporation of America, a corporation of Dela- Ware Filed Dec. 8, 1961, Ser. No. 158,012 19 Claims. (Q1. 29473.1)

This invention relates to electron discharge tubes and more particularly to a method of fabricating mount assemblies for such tubes.

One form of recently designed electron tube in which my invention is particularly useful includes a mount assembly comprising a flat wafer or disk header made, for example, of a ceramic material such as forsterite and having openings therethrough. The walls of said openings are coated with a suitable bonding material such as molybdenum. Lead-inand support conductors, preferably of molybdenum, extend through the openings in the Wafer and are employed to support and make electrical contact to the electrodes of the electron tube. The tube electrodes may comprise a plurality of concentrically disposed tubular elements, each having affixed to one end thereof an electrode support flange. The flanges, in turn, are fixed to and supported by the conductors, several conductors engaging each flange. Each flange is formed with a central tubular portion which is adapted to receive an end portion of an electrode to be supported thereby.

It is necessary to obtain vacuum tight seals between the conductors and the metallized walls of the holes in the ceramic header, and to rigidly secure the conductors to the electrode support flanges, and the flanges to the electrodes. To do this, brazing material is provided, which upon heating of the mount assembly previously assembled in a jig in loose contacting relationship, melts and flows to form the necessary joints between the mount assembly parts.

In the prior art, it is the practice to provide the brazing material for each joint in the form of rings or platings which are applied to the mount assembly parts in the vicinity of each brazed joint to be formed. One problem with this method, however, is that for a large number of joints to be brazed, a large number of separate brazing material sources have to be provided. The provision of these many brazing material sources has proven to be time consuming and expensive. For the brazing of the conductors within the ceramic wafer openings, for example, prior art practice is to provide a number of rings of brazing material each of which is threaded over a conductor and positioned adjacent the wafer. Upon heating, the rings melt and flow into the openings to provide the brazed joints. In one electron tube of this type, for example, eleven conductors each having a diameter of .016 inch are used, and eleven brazing rings having an outer diameter of .045 inch are required. Manual threading of these tiny rings onto the conductors is a difficult and tedious process. Further, even though automatic threading devices have been developed, the use of these devices still involves undesirable extra handling and assembling operations of the wafer, conductors, and brazing rings. Also, although conductors plated with the brazing material have been used, this method reduces the clearance between the conductors and the metalized holes in the wafer causing difliculty in threading the conductors through the holes.

Therefore, it is one object of this invention to provide an improved method of brazing together parts of a mount assembly for an electron tube.

More particularly, it is an object of this invention to provide a method of brazing together a number of parts of a mount assembly wherein the number of brazing ma- 3,Zfl8,l37 Patented Sept. 28, 1965 ice terial sources is greatly reduced, and wherein the expense and difliculties of providing the necessary brazing material are greatly reduced.

The prior art method of assembling mount assemblies of the type described involves the use of a jig adapted to receive and support individual tube parts. The jig includes a number of jigging cylinders adapted to receive successively the tubular electrodes in vertical position and in concentric, suitably spaced relation. Jig bottom portions are provided on which the lower ends of the electrodes rest, the bottom portions having predetermined heights with respect to a horizontal reference plane. The flanges may be loaded into the jig simultaneously with the electrodes or later. The flanges engage and rest on the upper ends of the electrodes, the ends of the electrodes being received within the tubular portions and engaging stop means provided in the tubular portions. A subassem-bly consisting of a wafer, heater and two conductors is then inserted into the jig, jigging means being provided for locating the wafer coaxially with the electrodes and at a predetermined distance from the reference plane. The remaining conductors are inserted into the wafer openings and drop downwardly until they engage the electrode flanges. The conductors extend from the flanges through the wafer and upwardly therefrom, the extending length of certain ones of the conductors from the wafer serving as socketing leads for the electron tube. The balance of the conductors are used only as supporting studs for the flanges.

A problem encountered in the prior art assembly of such mount assemblies is the difficulty of providing leads which extend a proper distance upwardly from the wafer. This requirement, as known, is necessary for providing proper electrical and mechanical connection of the leads with the tube socket. For conductors of given lengths, the extending lengths of the leads of electron tubes of the type described are determined by the distances between the flanges and the wafer. The Wafer is mounted directly on the jig, hence its position is controlled very accurately. The flanges, however, are mounted on the electrodes, hence their positions are dependent upon the tolerances in the electrode lengths. It has been found that these tolerances, combined with the tolerances of the flanges, frequently cause excessively large variations in the spacings of the flanges with respect to the reference plane. Such variations cause corresponding variations in the extending lengths of the leads. Prior art practice to solve this problem is to use longer leads than required and to trim all the extending leads to the correct lengths. This trimming operation, however, adds extra cost to the tube.

A further difliculty encountered in the fabrication of mount assemblies of the type described is the avoidance of tilting of the electrode support flanges with respect to each other and the electrodes. Such flange tilting causes variations in the wafer-flange spacings and variations in the extending lengths of the leads. Further, due to the flange tilt, the lengths of the several leads extending between the wafer and into contact with the tilted flanges are unequal. Upon brazing, the leads become rigidly fixed to the wafer and flanges before the mount assembly is fully cooled. Upon further cooling, the leads of unequal length secured to the tilted flanges contract different amounts thereby inducing stresses between the leads and the flanges. Such stresses tend to tilt the flanges thereby pressing the electrode brazed to each of the flanges against the jigging cylinder containing the electrode. Such pressing tends to destroy the concentric relationship of the electrodes While causing dragging and distortion of the electrodes against the jigging cylinders upon removal of the mount from the jig.

Prior .art practice, as mentioned, is to engage and rest the flanges on the upper ends of the electrodes, the ends of the electrodes being received within the tubular portions. In an attempt to provide proper tilt-free balancing of the flanges on the electrode ends, stops or positioning means are provided in the form of inwardly directed lips at one end of the tubular portions. Also, the dimensions of the tubular portions and the electrode ends are chosen so that there are relatively snug fits therebetween.

One disadvantage of this prior art practice is that it has been found very diflicult to provide the desired snug fit between the tubular portions of the flanges and the electrode ends. For one thing, the small tolerances required to provide these snug fits makes the parts diflicult and expensive to fabricate. Also, it has been found especially .diflicult to form the tubular portion lips with sufliciently smrall radius so as to provide positive stop means between the tubular portions and the electrodes. That is, rather than being formed as a sharply defined lip, the lips are often formed with a relatively large radius, the curved lip allowing the flange to roll and tilt with respect to the electrode end.

A further reason for the difliculty of obtaining the snug fit between the flanges and electrodes is the prior art practice of providng brazing material as a coating on the inside surface of the flange tubular portions. Thus, even if an electrode end is received snugly within a flange tubul ar portion during mount assembly, upon heating, the brazing material melts and flows and decreases the tightness of fit between the electrode end and the tubular portion by an amount equal to the thickness of the brazing material coating. Further, because the flange is normally of one material and its associated electrode of a different material, the flange material having a larger coeflicient thermal expansion, the flange tubular portion expands to a larger extent than the electrode end during brazing thereby further decreasing the tightness of fit.

It is therefore another object of this invention to provide an improved method of assembling mount assemblies of the type described wherein the above problems are avoided.

Particularly, further objects of this invention are to provide an improved method of assembling mount assemblies of the kind described wherein the length of the socketing leads may be accurately controlled; wherein tilting of the flanges with respect to the tube electrodes is avoided; and wherein a snug fit between the flange tubular portions and the electrode ends is provided both at room temperatures and at elevated temperatures.

In accordance with this invention, the surfaces of the conductors, the walls of the wafer openings, and in some instances, the flanges, are treated so as to make them very wettable by the brazing material. Such treatment may comprise mechanically scoring or etching the surfaces of some of these parts to provide pitted, roughtened surfaces thereon to promote capillary action for improving the flow of the molten brazing material. Also, the surfaces of some of the parts may be plated with a material that is very wettable by the brazing material. In the case of a brazing material comprising, for example, copper, the molybdenum conductors and molybdenum metalized header walls may be flash coated with iron, and in some instances, a further flash coating of copper.

During assembly of the mount assembly parts in the jig, the brazing material is provided on one surface of the flanges in the form of brazing rings, or the like (or provided as a prior plating or cladding on one surface of the flanges), and the loaded jig then heated to brazing temperature. The brazing material melts and flows along the treated surfaces to supply brazing material from each flange to all the joints in contacting relation with the flange. Advantages of this arrangement are that the brazing material need not be provided within the tubular portion of the flanges, the necessary brazing material flowing therein from the outer surface of the flanges; the need for all the conductor brazing rings for the conductors which are in contact With the flanges is avoided; and, as

will be described hereinafter, the coverage of the parts by the brazing material results in improved surface conditions thereof.

In practicing this invention electrodes and flanges are preferably employed in which the wall of the tubular portion of the flanges is conically shaped, tapering inwardly away from a face of the flange, and the lip of the prior art flanges is eliminated.

Preferably, in the assembly of the mount assembly parts, the larger end of the tubular portion is first accurately sized to an inner diameter which corresponds t the outer diameter of the electrode end to be inserted therein. Each electrode and its associated flange may be assembled onto a transfer quill, the electrode end being adjacent the larger diameter end of the tubular portion, and the flange-electrode pairs then inserted into the mounting jig. By means to be described, the flanges are pressed onto the ends of the electrodes, the tubular wall at the ends of the electrodes being deformed inwardly and decreased in diameter as the electrode ends are forced inwardly of the flange conical tubular portions. Since no lip or stop means are provided Within the tubular portions, the flanges may be pressed downwardly onto the electrodes any desired amount. By these means, the flanges may be accurately positioned with respect to the reference plane independently of the lengths of the electrodes. Also, since the electrode ends are forced inwardly of the tubular portions, a press, force fit therebetween is provided, the tightness of fi-t being suflicient to maintain a snug fit between the flanges and the electrodes even at elevated temperatures. Further, as will be described hereinafter, the flange pressing means assembles the flanges onto the electrode ends in perfect perpendicular relation while the force fit of the eelctrodes within the flange tubular portions insures complete and uniform peripheral brazing of the electrodes to the flanges.

Further features and advantages will become apparent as the description proceeds with reference to the attached drawings wherein:

FIG. 1 is a vertical section of an electron tube of the type in which my invention has utility;

FIG. 2 is a bottom plan view taken along line 2--2 of FIG. 1;

FIG. 3 is a longitudinal section of a brazing jig in which certain parts of the electron tube of FIG. 1 are shown mounted ready for the brazing o eration;

FIG. 4 is a vertical section of a portion of apparatus for pro-sizing the flange tubular portions in accordance with this invention;

FIG. 5 is a longitudinal section of a nest used for preassembling an electrode and its associated flange onto a transfer quill;

FIGS. 6 through 8 are longitudinal sections of a portion of the brazing jig shown in FIG. 3 illustrating the method of mounting a flange onto the end of a grid electrode in accordance with this invention;

FIG. 9 is a partial view in section of a wafer, a leadin, a flange, and an electrode prior to brazing;

FIG. 10 is a view similar to FIG. 11 but after braz- FIG. 11 is a View similar to FIG. 12 but showing the effects of modifications in flange construction and surface treatment; and,

FIG. 12 is an enlarged partial section of a conductor and a flange shown prior to brazing.

In FIG. 1 a completed electron tube of a type in the assembly of which the method of my invention has utility is shown. The tube 10 includes a ceramic disk header or wafer 12 having a plurality of bores 14 therethrough. A plurality of electrode support and lead-in conductors 16 and 17 are sealed in vacuum-tight relation in the bores 14.

As shown in FIG. 2, the bores 14 are arrayed in four concentric circles 18, 20, 22 and 24 shown in dotted line. Three bores 14 are disposed in equisdistant, relation on each of the circles. The bores in adjacent circles are angularly displaced 60 to provide maximum spacing therebetween.

The electron tube comprises coaxial tubular anode, grid, and cathode electrodes 26, 28 and 30, respectively. The grid electrode 28 comprises a plurality of parallel side rods 29 having a lateral wire 31 wound thereabout. The anode 26 is mounted on a radially extending flange 32, which is in turn mounted on three conductors 16 extending through bores 14 in the outer wafer circle 24. The grid electrode 28 is similarly mounted on a radially extending flange 34 which is in turn mounted on three of the conductors 16 extending through bores 14 on the circle 22. The cathode 30 comprises a cathode support sleeve 36 mounted on a radially extending flange 38, which is supported on three of the conductors 16 extending through the three bores on the circle 20.

As shown in FIG. 3, the flanges 32, 34 and 38 have centrally disposed tubular or cup-like portions 40 for receiving end portions of the electrodes referred to. The walls of the tubular portions are funnel-like or conically shaped, the walls tapering inwardly away from the face 41 (FIG. 4) of the flanges. Although shown quite pronounced, the amount of taper of the walls is actually very slight, the taper in one embodiment being only .020 inch of taper for one inch of length. Troughs 42 are provided at the peripheries of the flanges. The purposes of these troughs, as will be described hereinafter, is to insure relatively large area contact between the support conductors 16 and the molten brazing material during brazing.

The cathode 30 includes an emissive sleeve 43 (FIG. I) which is disposed over and sintered to the support sleeve 36, and which is coated with a suitable electron emissive material. A coiled heater 44 is disposed in the cathode support sleeve 36 and connects to a pair of the conduc tors 17 which are sealed through two bores 14 on the inner circle 18. A vacuum-tight envelope is provided by a cup-shaped shell 46 which is sealed to the periphery of the ceramic disk header 12. The shell 46 includes a pair of extending arcuate tongues 47 and 48 which serve to protect the externally extending conductors 16 and facilitate socketing of the tube. Both of the conductors 17 connected to the heater 44 extend through the ceramic header 12 and form socketing leads. Only one conduc tor 16 of each of the set of three conductors connected respectively to the anode, grid and cathode flanges extends through and beyond the ceramic header 12 to provide socketing leads.

In one form of the tube 10, the conductors 16 and 17 and the side rods 29 of the grid 28 are made of molybdenum, the side rods having a coating of nickel thereon; the cathode support sleeve 36 is made from a nickelchrome alloy; the anode 26 is nickel; and the flanges 32, 34 and 38 are steel.

The selection of these materials is dependent upon many diverse factors. The grid side rods 29, for example, are made of molybdenum because of the strength of this material and because of its high thermal conductivity. The former property is important because of the inherently fragile nature of wound grids of the type shown, and the latter property is important because of the necessity of efficiently removing the heat radiated to the grid from the cathode. The reason for the nickel coating will be discussed hereinafter. The collars are made of steel because of the wettability of steel by copper, and because it is relatively inexpensive. Similar reasons exist for the choice of the other materials mentioned.

Thus the flanges and the electrodes supported thereby are not made of the same materials. Hence, upon heating of the tube for brazing the parts, as mentioned, unequal expansion of the parts results.

In the fabrication of the electron tube 10 shown in FIG. 1 a rigid, unitary mount assembly is pre-assembled which includes the anode 26 and grid 28 electrodes and the cathode support sleeve 36, the respective electrode flanges 32, 34, 38 and conductors 16, the heater 44 and its conductors 17, and the ceramic wafer 12. Fabricating steps which may be employed in the fabrication of mount assemblies in accordance with this invention may include: preparing the surfaces of certain ones of the tube parts to make them especially wettable by a brazing material such as copper, accurately pre-sizing the tubular portions 40 of the flanges so that the larger inner ends 50 (FIG. 4) thereof are sized to a diameter which closely corresponds to the outer diameters of the ends of the electrodes to be inserted therein, pre-assernbling each electrode and its associated flange on a quill, inserting each flange and electrode pair into a brazing jig, force fitting the flanges onto the electrodes, adding brazing material to each flange, inserting the wafer including the heater and its conductors into the jig, inserting the remaining conductors through the wafer bores and into contacting relation with the flanges, and subjecting the loaded brazing jig to an elevated temperature for melting the brazing material and causing flow of the molten brazing material for providing the necessary brazed joints. Certain of these steps listed above may be omitted and certain ones rearranged in order. Each of these steps will now be described in detail.

The surfaces of certain ones of the mount assembly parts referred to are made readily wettable by the brazing material. This is done to permit adequate flow of the brazing material from a single brazing material source applied to one mount assembly part to all the parts in contacting relation therewith. In this embodiment, the brazing material is copper and, as mentioned, the flanges 32, 34 and 38 are made of steel, the conductors are made of molybdenum, and the metalized coating on the walls of the wafer bores is also of molybdenum.

For enhancing the flow of molten copper along the surface of the conductors 16, the molybdenum conductors may be etched by any known etching process. One such process, for example, is to make the conductors anodic within a 25-30% solution by weight of potassium hydroxide in water for 15-30 seconds, and then to make the conductors anodic within a second solution by weight of 10% potassium hydroxide and 1030% potassium ferricyanide in water for another 1530 seconds. The effect of these steps is both to etch and clean the conductors. Because of the manner in which the conductors are fabricated, that is, by drawing, the grain structure of the conductors is such that the etching process produces tiny valleys or grooves which extend longitudinally of the conductors. These tiny valleys serve as capillaries for conducting the molten brazing material up the conductors and into the bores 14 of the ceramic wafer 12.

An alternate method of treating the conductors to promote capillary action and improved flow of the brazing material therealong is to scratch and roughen the surface of the conductors. One method is to pass wire from which the conductors are to be cut through a box containing tightly packed abrasive particles.

The Wettability of the conductors and the molybdenum metalized walls of the wafer bores may be enhanced, either with or without surface roughening, by coating the surfaces with a flash of iron, iron being very wettable by copper as known. This coating may be accomplished by any suitable plating method such as electroplating, vapor deposition, and the like. While other materials such as cobalt and palladium produce nearly the same action as iron, the speed and uniformity of the flow of the brazing material seems to be best when iron is used. Furthermore, cobalt and palladium are more expensive than 115011.

The thickness of the iron flash or coating appears to have a definite affect on the flow of copper along a surface of molybdenum. It has been observed that optimum copper flow occurs when the iron coating is .7 to 1% of the weight of the molybdenum conductor. The copper flow may be even further improved by adding a .752.5% by weight flash of copper on top of the iron coating.

Since it is desirable that the brazing material for making all the brazed joints be provided from a minimum of sources, it is necessary that a suflicient amount of brazing material be provided in each source to cover the areas of the mount assembly parts over which the copper must flow. For this reason it has been found most convenient to provide the brazing material to the flanges 32, 34, 38 either in the form of large brazing rings 52 (FIG. 3) or as a coating of brazing material 53 (FIG. 9). For reasons to be described, the brazing material is provided only on one side of the flanges. During assembly of the amount assembly, as will be described, the flanges 32, 34, 38 (FIG. 3) are oriented so that the tubular portions 40 thereof extend upwardly as shown in FIG. 3, the troughs formed at the junction of the radially extending portions of the flanges 32, 34, 33 and the outside wall of the tubular portions providing convenient positioning and receiving means for the brazing rings 52. If the flanges are made of steel which is copper clad on one side, the brazing rings may be eliminated.

Since an object of this invention is to maintain the snug fit between the tubular portions of the flanges and the electrode ends at elevated temperature, the brazing material when supplied as a coating 53 (FIG. 9) to the flanges is applied only to the outer surface 54 of the flanges as shown in FIG. 9. That is, the brazing material should be applied to the flanges in such manner that no brazing material is provided on the inside walls of the tubular portions 40 which would melt and flow during brazing. As mentioned, this prevents a loosening of fit between the electrode ends and the tubular portions upon melting of the brazing material.

For providing such flanges, the flanges may be formed from copper clad steel stock, the copper and steel layers being pressed and forged together according to known cladding techniques. In .006 inch thick flange stock, the copper layer may be .002-.003 inch thick.

During brazing, it has been found that the copper flows from the outside of the tubular portions to the inside thereof thereby providing the brazed joint between the tubular portion and the electrode end contained therein. Various means may be employed, however, to enhance this flow and improve the dependability of the brazing operation.

One such means may comprise etching the uncoated surfaces of the flanges. The etching processes produces roughened pitted surfaces which, along with the natural aflinity of copper to steel, promotes complete distribution of the molten copper from the clad surfaces over the unclad surfaces. If the unclad steel surfaces are smooth and unetched, it has been found that the flow of molten cop per along the flanges may be inadequate even in a reducing atmosphere such as hydrogen. The flange etching may be performed using an etchant which does not attack copper. Such an etchant may comprise, for example, a 10% solution by weight of sulphuric acid and 5% of a commercially available inhibiter known as Enthone Stripper N165S.

Another means for promoting flow of the brazing material from outside the flange tubular portion to the inside thereof is to provide tiny holes 56 (FIG. 9) in the wall of the tubular portions through which the molten brazing material may flow.

In the instance wherein a copper brazing ring 52 is used without the provision of holes 56 through the flange tubular portion walls, the entire flange may be etched to promote the necessary flow of the molten copper over the flange surfaces. The etching may be performed by immersing the flanges in a cold 5% solution of nitric acid for two or three minutes.

After the surface treatment of the parts referred to, all the amount assembly parts are assembled together in a brazing jig. For reasons to be described, the step of pre-sizing the tubular portions 40 of the flanges is done as a part of the mount assembly process.

The flanges, as mentioned, are sized so as to make the inner diameter of end 50 (FIG. 4) thereof closely correspond to the outer diameter of the electrode end to be inserted therein. The flanges may be fabricated by conventional means such as by progressive dies or eyelet machines, and as initially fabricated, are provided with tubular portions 40 having a taper of 20 mils per inch with the inner diameter of ends 50 being about 0.002.004 inch smaller than the nominal outer diameter of the elec trode end to be inserted therein. The tolerance of the flanges as initially provided need not be very tight since the flange sizing operation provides the desired dimensional control over the tubular portions of the flanges, as will be described.

Apparatus for sizing the flange tubular portions 40 is shown in FIG. 4 and includes a platform 58 and a tapered pin 60 slidably mounted within bearings, not shown. Although not shown, means for adjustably and accurately controlling the downward movement of tapered pin 60 with respect to platform 58 may comprise any one of many simple stop means known in the mechanical arts. Tapered pin 60 has a 20 mil per inch taper.

In operation, a flange is positioned on platform 58 and pin 60 is inserted through the tubular portion 40 to stretch the wall of the tubular portion and increase the diameter thereof to a predetermined amount, the conical shape of the tubular portion being unchanged. The 20 mil per inch taper of pin 60, it is noted, provides a 50 to 1 ratio between pin insertion and tubular portion sizing whereby extremely fine and accurate sizing of the tubular portion inner diameter is achievable. That is, by controlling the insertion of pin 60 into the tubular portions to a tolerance of only .001 inch, for example, the sizing of the inner diameter of the tubular portions is controllable to a tolerance .00002 inch. Thus, for all practical purposes all variations in the inner sizes of the flange tubular portions is done away with whereby the only source of misfit between the electrodes and the tubular portions is that caused by the dimensional variations of the electrodes.

In accordance with another feature of this invention, however, even the misfits caused by the electrode tolerances are eliminated. This is accomplished in two ways.

Firstly, as mentioned, the tubular portions are sized so that the inner diameter of the larger end 50 thereof corresponds almost exactly to the nominal outer diameter of the electrode to be inserted therein. The length of the tubular portions 40 and the amount of taper are chosen so that the diameter of the smaller ends 55 thereof are always less than the outer diameters of the ends of the electrodes to be inserted therethr-ough. For an electrode having, for example, an outer diameter tolerance of plus 0, minus .0005 inch, a flange having a .030 inch long tubular portion may be used. With a 20 mil per inch taper, the diameter of the smaller end 55 of the tubular portion is .0006 inch smaller than the larger end 50 thereof and at least .0001 inch smaller than the elec trode outer diameter. Hence, upon forceful insertion of the electrode into and through the conical tubular portion, the electrode wall is squeezed and deformed inwardly. A tight press fit between the electrode and the flange thus always results, the electrode dimensional variations being absorbed by the deformation of the electrode wall.

Secondly, to further reduce the effects of the electrode tolerances, the flange sizing is done during mount assembly. This is done because although electrodes of the types described may be fabricated within small tolerances, average or statistical dimensional variations will exist between different batches of electrodes. This is due to slight variations in the materials used for the different electrode batches and changes in the fabricating apparatus due to wear and changing environmental conditions, and the like. By adjusting the flange sizing at mount assembly, corrections in the fit of the flanges with the electrodes 9 may be made immediately as required. Since the amount of flange sizing is adjustably and accurately controllable, the result is that the flanges may be practically custom fit to their corresponding electrodes.

A still further advantage to this method of pre-sizing is that it is possible to make small changes in electrode dimensions for engineering tests, and the like, without requiring new tooling for the fabrication of flanges of the proper size. That is, small electrode diameter changes may be compensated for by changing the amount of flange sizing. Also, elimination of the prior art tubular portion lips simplifies fabrication of the flanges.

After the flanges are sized, each flange is preassembled in loose contacting relationship with its associated electrode. To accomplish this, nests 62. of the type shown in FIG. may he provided. Nest 62 comprises a tubular portion 63 having a stop portion 64 at one end thereof for receiving a tube electrode in vertical orientation (a grid electrode 28 in this instance), and a second tubular portion 65 coaxial with tubular portion 63 for receiving and positioning a flange 34 coaxially with the grid electrode. A transfer quill 68 having a slightly tapered portion 69 is inserted through the tubular portion 46 of the flange 34 and through and into contact with the grid electrode 28. The electrode with the flange resting thereon adheres to the tapered quill portion 69, the electrode-flange pair being lifted out of the nest 62 upon retraction of the quill. Nest 62 is then removed from beneath the transfer quill, and a brazing jig 72 is positioned in its place.

In FIG. 3 a brazing jig 72 is shown. The jig 72 comprises a cup-like housing 73 which includes a circular cup base 74 and a hollow circularly cylindrical cup wall 75. Two hollow cylindrical jigging elements 76 and 77, coaxial with the cup wall 75, extend from the cup base 74 within the cup 73. The cup base 74, the cup Wall 75 and the jigging elements 76 and 77 may or may not be provided as an integral structure.

The inner cylindrical jigging element 76 has a diameter such that it can receive in snug contacting relation therein the cathode support sleeve 36. The wall thickness of the inner jigging element 76 is such that the grid 28 of the electron tube 16 can be snugly received therearound in a desired spacing of the grid 28 from the cathode support sleeve 36. The size of the outer jigging element 77 is such that it can receive in snug contacting relation therewithin the anode 26, the anode being spaced a predetermined distance from the grid 28.

The brazing jig 72 also includes a hollow cylindrical insert support 86 which is adapted to be received coaxially within the cup wall 75 in a loose fit therewith. The ceramic disk header 12 is axially supported upon the end of the insert 80, which in turn rests on the cup base 74. The insert 80 is of a length suitable to provide a selected spacing of the ceramic disk header 12 from the top surface 78 of the cup base 74. Base bottom portions 82, 8'4, and 86 for receiving the ends of the electrodes 26, 28, 36, respectively, are also provided for providing selected spacings of the lower ends of the electrodes from the cup base surface 78.

In the assembly and fabrication of the electron tube 10, the jig 72 is oriented with the open end up. As shown in FIG. 6, the leading end 90 of the quill 63 is inserted into the inner cylindrical jigging element 76 of jig 72, the jigging element 76 serving to center the quill pilot 91 and the grid 28 and flange 34 adhered thereto with respect to the brazing jig. The quill pilot 91 is inserted fully into jigging element 76 until the leading end 90 engages a small shoulder or pad 92 on the cup base 74, the lower end of the grid electrode not quite reaching the jigging cylinder 76, as shown. A stripper plate 94 is then actuated downwardly by means not shown, the flat bottom surface 95 thereof being maintained perfectly square with respect to the longitudinal axis of the brazing jig. Bottom surface 95 engages peripheral portions of the 19 grid flange and exerts a uniform pressure on the flange to force it downwardly against the grid electrode, thereby disengaging the grid 28 and the grid flange from the tapered portion 69 of quill 68 and forcing the grid downwardly and fully into the jig as shown in FIG. 7.

The downward movement of the stripper plate 94 continues, and when the lower end of grid 28 engages the jig bottom stop 84, further movement of stripper plate 94 presses flange 34 downwardly against the upper end of the grid. The inner diameter of the larger end 50 of the flange tubular portion 40 has been sized to correspond to the outer diameter of the grid electrode, as mentioned, and the result of the flange pressure is that the ends of the side rods 29 are deformed inwardly and are forcibly inserted into the flange tubular portion 40 (FIG. 8). The forceful insertion of the side rods into the tubular portion results in a tight press fit therebetween, the tightness or snugness of fit being such as not to be significantly affected even at elevated temperatures. Since the grid is supported firmly with the jig 72 during flange insertion, and the flange pressed uniformly downwardly by stripper plate 94, the flange is mounted in perfect tilt-free relation on the end of the electrode.

A further feature of the method of assembly in accordance with this invention, is that the height of the flange 34 above a fixed reference plane, say the top surface 78 of cup bottom 74 (FIG. 3) may be controlled to a high degree of accuracy in spite of the manufacturing tolerances found in the length of the tube electrodes. That is, in the prior art tubes, as described, the flanges are perched on top of the ends of the electrodes, the location of the flanges with respect to the ends of the electrodes being fixed by engagement of the tubular portion lips with the electrode ends. According to this invention, however, it is possible to press the flanges onto the electrodes as far as desired, the inwardly deformed electrode walls passing through the conical tubular portion as shown exaggerated in FIG. 8. The advantage of this arrangement, as mentioned, is that the spacings between the flanges and the ceramic header wafer 12 may thus be accurately controlled, whereby the lengths of the conductors 16 extending outwardly of the wafer 12 may also be accurately controlled.

After the flange 34 has been inserted onto the grid electrode 23 to the proper height above the reference plane, the stripper plate 94 is held against the flange while the quill 68 is retracted from the jig, the stripper 94 then also being retracted.

Although not described, the steps of assembling the anode 26 and cathode 30 electrodes to their respective flanges 32 and 36, and inserting these flange-electrode pairs into the brazing jig 72, are performed in similar manner to the assembly and insertion of the grid electrode 28. Since the diameter of the anode, grid, and cathode electrodes decrease in size in the order named, however, these electrodes with their respective flanges must be loaded into the brazing jig in the order listed to permit telescoping loading of the electrodes therein.

If the flanges have not been provided with a cladding of brazing material, rings of copper 52 are dropped over the tubular portions of each flange as shown in FIG. 3. The header wafer 12 is then disposed in the jig cup 73 on top of the insert 80. Prior to this, two conductors 17 having brazing material rings 98 threaded thereon have been inserted into proper bores 14 in the ceramic disk header 12, and the coil heater 44 attached to the ends of the conductors. The brazing rings 98 are provided with conductors 17 since the aluminum oxide coated heater provides no wettable surface on which a larger, more conveniently handled brazing material source may be applied. Also, the header 12 has been prepared with a metallic coating of molybdenum, the coating covering the outer periphery 97 of the header and the walls of the bores 14. Such a coating may be applied by any suitable known metalizing process. It has been found expedient to coat all surfaces of the ceramic disk header 12 with molybdenum and then grind the two planar surfaces thereof to remove the coating therefrom. Thus, only the outer periphery 97 and the walls of the bores 14 are left with a metalized coating. The walls of the bores 14 have also been provided with an iron coating as previously described.

After insertion of the header 12 into the jig cup 73, the remaining nine conductors 16, three for each electrode flange, are loaded into their proper bores in the header 12. The conductors 16 are such that they fit snugly within the bores 14 but are nevertheless slidable therein so that they may drop downwardly and into contact with the peripheral trough portions 42 of their respective electrode flanges. The assembly of the jig 72 and the electron tube parts shown in FIG. 3 are then inserted in a furnace and heated in a reducing atmosphere to a temperature sufficient to melt the brazing material rings 52 or the coatings 53 on the flanges, 32, 34 and 38, and the heater conductor brazing rings 98.

As shown in FIGS. 9 and 10 wherein a flange having a copper cladding 53 thereon is used (the flange having holes 56 therethrough), the molten brazing material flows into the tubular portions 40 and up the conductors 16 and into the bores 14. Because of the firm contact between the electrode ends and the tubular portion walls due to the press fit therebetween, complete and uniform brazes are made around the entire outer periphery of the electrode ends and the tubular portions of the flanges. Also, the conductors 16 are brazed within bores 14, the conductors being entirely coated with brazing material.

The advantages of the complete and uniform peripheral brazing are that the complete peripheral brazes provide low thermal resistance paths for conduction of heat from the electrodes, and the uniform brazing avoids non-symmetrical brazing stresses which tend to tilt the electrodes and change the relative electrode spacings. Except for the brazing material which extends through the flanges via the holes 56, FIG. 10 also illustrates the end results when copper clad flanges are used, 53' representing the copper cladding material spread after the brazing.

FIG. 11 illustrates the end result in those instances when either a brazing ring 52 is used or when a coated, etched flange is used. The difference from the end result illustrated in FIG. 10 is that the entire flange in FIG. 11 is coated over with brazing material 53' due to the wettability of the etched flange surfaces.

As mentioned, the purpose of the flange peripheral troughs 42 is to provide large area contact between the conductors 16 and the brazing material. Further, the flange troughs insure positive contact between the conductors and the flanges. It has been found that such contacts of the conductors 16 with the flanges and brazing material are necessary in order that the brazing material flow from the flanges up the conductors. Normally, as shown in FIG. 3, the lower ends of the conductors rest upon and engage the flanges thereby providing sufiicient contact between the conductors and the flanges and between the conductors and the brazing material when the brazing material is heated and melted. In some instances, however, the lower ends of the conductors may make only point contact with the flanges or make no contact at all with the flanges.

The former condition, as shown in FIG. 12, may arise due to the presence of slivers 102 extending outwardly from the end of the conductor 16. Such slivers, as known, frequently occur upon the cutting of molybdenum wire and, as shown, prevent contact of the lower end of the conductor with the flange. The latter condition (not shown) may arise as a result of the different thermal expansion of the mount electrodes. In some instances the conductors become tacked or sintered to the wafer before full brazing temperature is reached and before the conductors are secured to the flanges. This is especially possible when the conductors have a flash coating of cop per thereon. Upon further increase of temperature, one

electrode may expand more than the others thereby raising its flange and the conductors engaged therewith a distance greater than the other flanges and conductors are raised by their corresponding electrodes. Since the conductors are tacked to the wafer, the wafer is also raised thereby lifting all the other conductors away from their respective flanges.

As shown in FIG. 12, the purpose of the troughs 42, therefore, is to provide engagement between the lower edges of the conductor 16 and the trough wall even though the bottom end of the conductor is spaced out of contact with the flange. Although not shown, larger area contact between the conductors and the flanges may be achieved by providing troughs with rectangular cross sections, that is, with vertically extending side walls. With such troughs, side surfaces of the conductors rather than just the edges thereof will engage the trough walls. Although a snug fit of the conductors within the troughs is not provided, the loosely inserted conductors will generally engage either one or the other side walls of the thoughs. Further, upon brazing, melted brazing material collects and forms pools in the troughs. These pools (indicated by dash line 104 in FIG. 12) contact side surfaces of the conductors thereby further enhancing flow of the brazing material therealong.

Further advantages of this method of brazing are that due to the increased wettability of the conductors, as provided by the means described, the copper provides highly desired large radii at the cut ends of the conductors eliminating the sharp edges thereof. This reduces wear of sockets in which the tubes are inserted. Moreover, the uniform coating of the parts due to the flow of the copper thereon decreases electrical contact resistance, improves the appearance of the external parts of the tube, and makes the conductors more resistant to corrosion.

It is noted that the brazing material does not flow down the electrodes due to the fact that the electrodes are made of nickel or of an alloy containing nickel. Upon contact of molten copper to nickel, an alloy of the two materials is formed which has a higher melting point than copper itself. Since it is desired to prevent wetting of the electrodes, which would interfere with the electrical operation of the tube, the temperature of the brazing furnace is maintained at a temperature suflicient to melt copper but not high enough to melt the coppernickel alloy. This provides for stoppage of the copper flow at the point of alloying.

Following brazing, cooling, and removal of the mount assembly from the brazing jig, the cathode emissive sleeve 43 is placed over the cathode support sleeve 36 and the envelope shell 46 is fitted in contact with the ceramic header 12. A preformed ring of a hard solder is positioned in contact with the tube shell 46 and the ceramic header periphery 97.

This assembly results in a complete tube assembly which is then subjected to a final furnace heating in vacuum. This final processing step serves to evacuate the tube, sinter the cathode emissive sleeve 43 to the cathode support sleeve 36, and solder the shell 46 to the periphery 97 of the header 12. The temperature employed in this final step is substantially below the previous brazing temperature. Accordingly, the previously made brazes are not affected.

What is claimed is:

1. Method of brazing together parts of a mount assembly including a ceramic wafer having an aperture therein, a conductor extending through said aperture, a flange supported on said conductor, and an electrode supported on said flange, said method comprising providing surfaces wettable by a brazing material on said conductor and the wall of said aperture, assembling said mount assembly parts into contacting relation, applying brazing material only to said flange, and subjecting said assembly to a brazing temperature suificient to cause said brazing material to melt and flow over said flange and said conductor to provide brazed joints between said assembled parts including a brazed joint between the walls of said aperture and said conductor.

2. Method of brazing together parts of a mount assembly including a ceramic wafer having an aperture therein, a conductor extending through said aperture, a flange supported on said conductor, and an electrode supported on said flange, said method comprising providing a pitted and roughened surface on said conductor, coating said conductor and said aperture wall with a material wettable by a brazing material, assembling said mount assembly parts into contacting relation, applying brazing material only to said flange, and subjecting said assembly to a brazing temperature suflicient to cause said brazing material to melt and flow over said flange and said conductor to provide brazed joints between said assembled parts including a brazed joint between the walls of said aperture and said conductor.

3. Method of brazing together parts of a mount assembly including a ceramic wafer having an aperture therein, a conductor extending through said aperture, a flange supported on said conductor, and an electrode supported on said flange, said method comprising treating said flange and said conductor for providing pitted and roughened surfaces thereon, coating said conductor and said aperture wall with a material wettable by a brazing material, assembling said mount assembly parts into contacting relation, applying brazing material only to said flange, and subjecting said assembly to a brazing temperature suflicient to cause said brazing material to melt and flow over said flange and said conductor to provide brazed joints between said assembled parts.

4. Method of brazing together parts of a mount assembly including a ceramic wafer having an aperture therein, a conductor extending through said aperture, 2. flange supported on said conductor, and an electrode supported on said flange, said method comprising etching said conductor for providing a roughened surface thereon, flashing said conductor and said aperture wall with a material wettable by a brazing material, assembling said mount assembly parts into contacting relation, applying brazing material only to said flange, and subjecting said assembly to a brazing temperature sufiicient to cause said brazing material to melt and flow over said flange and said conductor to provide brazed joints between said assembled parts.

5. Method of brazing together parts of a mount assembly including a ceramic wafer having an aperture therein, a conductor extending through said aperture, a flange supportingly engaged with said conductor, and an electrode supportingly engaged with said flange, said method comprising applying a coating of brazing material only to said flange, etching said flange and said conductor for roughening the surfaces thereof, providing a coating of a material wettable by said brazing material on said conductor and the wall of said aperture, assembling said mount assembly parts into contacting relation, and subjecting said assembly to a brazing temperature sufficient to cause said brazing material to melt and flow from said flange along said conductor to provide brazed joints between said assembled parts.

6. Method of brazing together parts of a mount assembly including a ceramic wafer having an aperture therein, a conductor extending through said aperture, a flange having a first surface thereof engaged with said conductor, and an electrode engaged with a second surface of said flange, said method comprising applying a coating of brazing material only to said first surface, roughening the surface of said conductor, providing a coating of a material wettable by said brazing material over said conductor and the wall of said aperture wall, assembling said mount assembly parts into contacting relation, and subjecting said assembly to a brazing temperature sufficient to cause said brazing material to melt and flow from said first surface to said second surface and along said conductor for providing brazed joints between said assembled parts.

7. Method of brazing together parts of a mount assembly including a ceramic wafer having an aperture therein, a conductor extending through said aperture, 21 flange having a first surface thereof supportingly engaged with said conductor, and an electrode supportingly engaged with a second surface of said flange, said method comprising applying a coating of brazing material only to said first surface, etching said second surface and said conductor for roughening the surfaces thereof, providing a coating of a material wettable by said brazing material over said conductor and on said aperture wall, assembling said mount assembly parts into contacting relation, and subjecting said assembly to a brazing temperature sufficient to cause said brazing material to melt and flow from said first surface to said second surface and along said conductor for providing brazed joints between said assembled parts.

8. Method of brazing together parts of a mount assembly including a ceramic wafer having an aperture therein, a conductor extending through said aperture supportingly engaged with said conductor, and an electrode supportingly engaged with said flange, said method comprising applying brazing material only to said flange, treating the surface of said conductor and the wall of said aperture to snake the said conductor surface and aperture wall wettable by said brazing material, assembling said mount assembly parts into contacting relation, subjecting said assembly to a brazing temperature suflicient to cause said brazing material to melt and form a pool on said flange and in contacting relation with said conductor whereby said brazing material flows along said conductor.

9. Method of providing a rigid mount assembly including a tubular electrode and a support flange having a funnel-like tubular portion, the inner diameter of the smaller end of said tubular portion being slightly less than the outer diameter of an end of said electrode, said method comprising engaging said electrode end with the larger end of said tubular portion, pressing said flange onto said electrode end whereby said electrode end is deformed inwardly to permit passage of said electrode end inwardly of said tubular portion, and passing said electrode end through said tubular portion until the distance between said flange and the other end of said electrode is reduced to a preselected value.

10. Method of providing a rigid mount assembly including a tubular electrode and a support flange having a funnel-like tubular portion, the inner diameter of the larger end of said tubular portion being slightly less than the outer diameter of an end of said electrode, the method comprising sizing said larger end of said tubular portion to a diameter corresponding to the outer diameter of said electrode end, engaging said electrode end with said sized tubular portion end, and pressing said flange onto said electrode end whereby said electrode end is deformed in- Wardly to permit passage of said electrode end inwardly of said tubular portion to provide a tight press fit therebetween.

11. Method of providing a rigid mount assembly including a tubular electrode and a support flange having a funnel-like tubular portion extending inwardly away from a face of said flange, the inner diameter of the larger end of said tubular portion being slightly less than the outer diameter of an end of said electrode, said method comprising sizing the larger end of said tubular portion to a diameter corresponding to the outer diameter of said electrode end, supporting said electrode in a jig, engaging said electrode end with said sized tubular portion end, pressing said flange onto said electrode end whereby said electrode end is deformed inwardly to permit passage of said electrode end inwardly of said tubular portion, and passing said electrode end through said tubular portion until the distance between said flange and the other end of said electrode is reduced to a preselected value.

12. Method of assembling tube parts into a mount assembly including a ceramic wafer having an aperture therethrough, a conductor extending through said aperture, a flange supported on said conductor, and a tubular electrode supported on said flange, said flange having a conical shaped tubular portion, the opening through the larger end of said tubular portion being substantially equal in size to the cross-sectional area of an end of said electrode, said method comprising treating the surface of said conductor and the wall of said aperture for making them wettable by a brazing material, forcibly inserting said end of said electrode into said larger end of said tubular portion thereby inwardly deforming said electrode end for providing a snug press fit between said flange and said electrode, assembling said wafer and said conductor in contacting relationship with said flange and said electrode, applying a brazing material only to said flange, and subjecting said assembly to a brazing temperature suflicient to cause said brazing material to melt and flow along said flange and said conductor to provide brazed joints between said assembled parts.

13. Method of assembling tube parts into a mount assembly including a ceramic wafer having an aperture therethrough, a conductor extending through said aperture, a flange supported on said conductor, and a tubular electrode supported on said flange, said flange having a conical shaped tubular portion extending from a face thereof, the opening through the larger end of said tubular portion being substantially equal in size to the crosssectional area of an end of said electrode, said method comprising treating the surfaces of said flange, said conductor, and the wall of said aperture for making them wettable by a brazing material, forcibly inserting said end of said electrode into said larger end of said tubular portion thereby inwardly deforming said electrode end for providing a snug press fit between said flange and said electrode, assembling said wafer and said conductor in contacting relationship with said flange and said electrode, applying a brazing material only to said flange and subjecting said assembly to a brazing temperature suflicient to cause said brazing material to melt and flow over said flange and said conductor to fill said tubular portion and said aperture and to provide brazed joints between said conductor and said wafer, between said conductor and said flange, and between said flange and said electrode.

14. Method of assembling tube parts into a mount assembly including a ceramic wafer having an aperture therethrough, a conductor extending through said aperture, a flange supported on said conductor, and a tubular electrode supported on said flange, said flange having a conical shaped tubular portion extending from a face thereof, said method comprising treating the surfaces of said conductor and the wall of said aperture for making them wettable by a brazing material, sizing the larger end of said tubular portion to correspond to the outer diameter of an end of said electrode, inserting said electrode end into said sized end of said tubular portion and forcing said electrode end inwardly thereof thereby inwardly deforming said electrode end for providing a snug press fit between said flange and said electrode, assembling said wafer and said conductor in contacting relationship with said flange and said electrode, applying a brazing material only to said flange, and subjecting said assembly to a brazing temperature suflicient to cause said brazing material to melt and flow over said flange and said conductor for brazing said assembled parts.

15. Method of assembling tube parts into a mount assembly including a ceramic wafer having an aperture therethrough, a conductor extending through said aperture, a flange supported on said conductor, and a tubular electrode supported on said flange, said flange having a conical shaped tubular portion extending from a face thereof, said method comprising roughening the surface of said conductor, coating said conductor and the wall of said aperture with a material wettable by a brazing material, sizing the larger end of said tubular portion to correspond to the outer diameter of an end of said electrode, inserting said electrode end into said sized end of said tubular portion and forcing said electrode inwardly thereof thereby inwardly deforming said electrode end for providing a snug press fit therebetween, assembling said wafer and said conductor in contacting relationship with said flange and said electrode, applying a brazing material only on the outside surfce of said tubular portion, and subjecting said assembly to a brazing temperature sufficient to cause said brazing material to melt and flow along said flange and said conductor for brazing said assembled parts.

16. Method of brazing together parts of a mount assembly including a ceramic wafer having an aperture therein, a conductor extending through said aperture, a flange supported on said conductor, and an electrode supported on said flange, said method comprising providing surfaces wettable by a brazing material on said conductor and the wall of said aperture, assembling said mount assembly parts into contacting relation with said conductor extending upwardly of said flange, applying brazing material only to said flange, and subjecting said assembly to a brazing temperature sufficient to cause said brazing material to melt and flow over said flange and upwardly of said conductor to provide brazed joints between said assembled parts including a brazed joint between the walls of said aperture and said conductor.

17 Method of brazing together parts of a mount assembly including a ceramic wafer having an aperture therein, a conductor extending through said aperture, a flange supported on said conductor, and an electrode supported on said flange, said method comprising providing a pitted and roughened surface on said conductor, coating said conductor and said aperture wall with a material wettable by a brazing material, assembling said mount assembly parts into contacting relation with said conductor extending upwardly of said flange, applying brazing material only to said flange, and subjecting said assembly to a brazing temperature sufficient to cause said brazing material to melt and flow over said flange and upwardly of said conductor to provide brazed joints between said assembled parts including a brazed joint between the walls of said aperture and said conductor.

18. Method of brazing together parts of a mount assembly including a ceramic wafer having an aperture therein, a conductor extending through said aperture, 21 flange supported on said conductor, and an electrode supported on said flange, said method comprising treating said flange and said conductor for providing .pitted and roughened surfaces thereon, coating said conductor and said aperture wall with a material wettable by a brazing material, assembling said mount assembly parts into contacting relation with said conductor extending upwardly of said flange, applying brazing material only to said flange, and subjecting said assembly to a brazing temperature sufficient to cause said brazing material to melt and flow over said flange and upwardly of said conductor to provide brazed joints between said assembled parts.

19. Method of brazing together parts of a mount assembly including a ceramic wafer having an aperture therein, a conductor extending through said aperture, a flange supported on said conductor, and an electrode supported on said flange, said method comprising etching said conductor for providing a roughened surface thereon, flashing said conductor and said aperture wall with a material wettable by a brazing material, assembling said mount assembly parts into contacting relation with said conductor extending upwardly of said flange, apply- 17 ing brazing material only to said flange, and subjecting said assembly to a brazing temperature sufficient to cause said brazing material to melt and flow over said flange and upwardly of said conductor to provide brazed joints between said assembled parts.

References Cited by the Examiner UNITED STATES PATENTS Dunn 29473.1 Ingram 29503 X Ammenwerth 29-2515 X McCullough et a1. 29-2516 X Zeller 29500 X Rhoads et a1 29473.1 Knauf et a1. 31619 Palmour 29-500 X Solow et a1 174-52 Lalok 29423 WHITMORE A. WILTZ, Primary Examiner.

LEON PEAR, JOHN F. CAMPBELL, Examiners. 

1. METHOD OF BRAZING TOGETHER PARTS OF A MOUNT ASSEMBLY INCLUDING A CERAMIC WAFER HAVING AN APERTURE THEREIN, A CONDUCTOR EXTENDING THROUGH SAID APERTURE, A FLANGE SUPPORTED ON SAID CONDUCTOR, AND AN ELECTRODE SUPPORTED ON SAID FLANGE, SAID METHOD COMPRISING PROVIDING SURFACES WETTABLE BY A BRAZING MATERIAL ON SAID CONDUCTOR AND THE WALL OF SAID APERTURE, ASSEMBLING SAID MOUNT ASSEMBLY PARTS INTO CONTACTING RELATION, APPLYING BRAZING MATERIAL ONLY TO SAID FLANGE, AND SUBJECTING SAID ASSEMBLY TO A BRAZING TEMPERATURE SUFFICIENT OT CAUSE SAID BRAZING MATERIAL TO MELT AND FLOW OVER SAID FLANGE AND SAID CONDUCTOR TO PROVIDE BRAZED JOINTS BETWEEN SAID ASSEMBLED PARTS INCLUDING A BRAZED JOINT BETWEEN THE WALLS OF SAID APERTURE AND SAID CONDUCTOR. 